Effects of cosolvent on dissolution behaviors of PVAc in supercritical CO2: A molecular dynamics study

The dissolution behavior of polymers in CO2 has become increasingly important to the applications of CO2 in industry. Experimental results showed that PVAc could be dissolved in CO2 at a high pressure. When cosolvents such as ethanol, acetic acid, and ethyl acetate were present in the system, the transition points could be decreased with the increase in cosolvent concentration. In this work, the influence mechanisms of cosolvents on dissolution behaviors of PVAc in supercritical CO2 were investigated by molecular dynamics simulation methods. First, the cohesive energy and solubility parameters of PVAc, cosolvents and CO2 were analyzed. Compared with CO2, the mixtures of CO2 and cosolvents have closer solubility parameters with PVAc to enhance the dissolubility of PVAc within them. Moreover, the mechanism of PVAc dissolution in CO2 and the effects of cosolvents on decreasing the transition points were investigated. The Lewis acid-Lewis base (LA-LB) interactions between 0 atoms in PVAc and C atoms in CO2 are the main influencing factors of PVAc dissolution in CO2. The presence of cosolvent can generate new interactions, such as hydrogen bonding and LA-LB interactions, which have different influences on the LA-LB interactions between PVAc and CO2. Ethanol and ethyl acetate have no great influence on these LA-LB interactions, while acetic acid exerts considerable influence. (C) 2019 Elsevier Ltd. All rights reserved.